I didn't even buy shoes for my children until they could stand; socks are fine on WDW rides. Once they can stand, full water sandals are the easiest option (and you should also wear them; we don't wear any other kind of shoe in Orlando parks in summer.)
I took mine to WDW several times as infants. Loose cotton sundresses are best, let that tummy get plenty of air.
Some things we found helpful:
1) flat cloth diapers; several of them. These are HUGELY versatile. You can use them as cooling cloths, as sun blockers, even tie two of them together at the corners as an emergency dress. Every morning I folded three of them inside a gallon ziploc bag with ice, which melted through the day, and I could use them to wipe down the baby to cool her off quickly if she was overheated. (And they are a godsend in the event of vomiting or a severe diaper blowout; they hold up to mopping up a large disaster in a way that paper towels just don't.)
2) handful of large binder clips, to secure the previously mentioned diapers to strollers or backpacks.
3) a 3-oz travel bottle filled with liquid detergent, so you can wash the previously mentioned cloth diapers if you need to do it when away from your hotel.
3) A light-colored mesh sling that we could wear to securely get her wet. Wore it in the pools and into the splash pads at the parks -- much easier to keep a secure hold on a slippery baby. The other children at the splash pads fascinated her, and the fountains were endlessly entertaining for her to watch. The sling is also the best option for taking a baby onto rides or through long ride lines where strollers are not allowed, as it can be swung to the side to make room for the lap bar. (It can be awkward to climb in or out of ride vehicles with a baby in arms; nicer to have a hand free.)
4) Extra gallon ziplocs to contain soiled clothing that has to be washed later.
5) Sunglasses for the baby. Florida sun is very bright, and all the concrete reflecting light can tire out little eyes. Get some that can be chewed, with full ear hooks.